1. Field of the Invention
The invention relates to a process for the preparation of nitrophenyl alkyl ethers from nitrophenols and alkyl halides in the presence of hydrogen halide-binding compounds, which is characterised in that water is used as the reaction medium, and also in that nitrophenol is laid before with the water and the alkyl halide and the hydrogen halide-binding compound are then added simultaneously,
Nitrophenyl alkyl ethers are important organic intermediates, for example in the preparation of dyes.
2. Description of the Related Art
Beilstein, 4th edition, Volume VI, p. 412 (1923), discloses the preparation of 2-nitro-4-methyl-phenyl methyl ether from dry 2-nitro-p-cresol in the form of the silver salt and methyl iodide diluted with ether.
Houben-Weyl, 4th edition, Volume VI/3 (1965), p. 54ff., discloses the alkylation of phenolates with alkyl halides in an aqueous medium. However, as soon as the phenolates bear a nitro group, this reaction is carried out in an organic solvent, such as cyclopentanone or xylene (loc. cit., p. 56). Fierz-David, Grundlegende Operationen der Farbenchemie (Fundamental operations in colour chemistry), 8th edition (1952), p. 143, also mentions methanol or ethanol as the reaction medium.
In addition, the use of another alkylation agent, that is dimethyl sulphate in conjunction with potassium carbonate using xylene as solvent, is known (Beilstein, 4th edition, Volume VI EI, p. 206).
Various disadvantages are associated with the processes of the prior art. Thus the introduction of all of the nitrophenol in the form of the phenolate is a safety risk, and, moreover, leads to problems on stirring and to a poor conversion rate owing to the poor solubility of the nitrophenolate. If all of the reactants are introduced together and completely, there is the danger of a spontaneous reaction in which the exothermic heat of reaction can no longer be removed rapidly enough. With the use of alcohols as reaction medium there is furthermore the danger of unwanted ether formation with the alkyl halide reactant.